Different systems for utilisation of waste heat of an internal combustion engines are known. The most commonly used solution is a so called combined cycle, where the waste heat of internal combustion engine is utilised in a separate steam engine. An example of such a solution is provided for instance in publication U.S. Pat. No. 5,133,298. This kind of solution is a relatively expensive and somewhat difficult also, as internal combustion engines differ strongly in size and each size range requires a different steam engine.
In number of patents, for instance in U.S. Pat. No. 4,377,934, U.S. Pat. No. 4,406,127, U.S. Pat. No. 4,706,468 and U.S. Pat. No. 4,901,531, different versions of the bottom steam cycle are proposed, in which at least one cylinder of the internal combustion engine is used as the steam power recovery device, which in fact is a modification of the classic combined cycle engines. In U.S. Pat. No. 4,433,548 the alternating use of same cylinders for combustion and steam power strokes is described. Further, in U.S. Pat. No. 4,409,932 injection of the steam during the power stroke i.e. after combustion is proposed in a petrol car engine. A negative feature of all these solutions is that the emissions of the combined systems are the same as for the internal combustion (top) engine.
Many publications, for example U.S. Pat. No. 3,761,019, U.S. 4,014,299, U.S. Pat. No. 4,027,630, U.S. Pat. No. 4,059,078, U.S. Pat. No. 4,391,229, U.S. Pat. No. 4,409,931 and U.S. Pat. No. 4,844,028, describe steam injection into an inlet manifold of engines to control power, knock or NOx-emissions. However, these solutions using low grade steam and leaving the energy transformations out of considerations, do not necessarily provide increased efficiency.
Turbochargers as such are developed to achieve high conversion efficiency of the exhaust gas energy into the energy of compressed air used in the engine. Total energy conversion efficiencies of modern turbocharger approach 70%. Typically few turbocharger families are available to cover the possible engine applications and thus turbochargers able to accommodate more energy are readily available as such.